Slow 'unlimited' fibre

[#1]

Hi,
My unlimited fibre is slow (d/l speeds less than 5mbs) and according to plusnet support page my line speed is showing as a feeble 6mbs.
BT DSL checker gives me a reported line speed of 80mbs! What gives?
Have done all the usual resetting router and BT fibre box, no difference.
A couple of years ago we had a problem with our account still being set to ADSL despite upgrading to fibre, could this be a recurrence of that?

Not sure what to do next!

Cheers!

[#2]

Thanks for your time on the phone just now, I've tested your line and as explained we're seeing evidence of a loop fault which can actually be caused by issues with your equipment so we need to rule that out next. 

As we agreed I'll test the line again at 5pm which is when the router will be unplugged from the line and I'll follow things up with you from there. 

[#3]

Hi Adam, can confirm all devices unplugged.
Cheers,

[#4]

Thanks, I've just responded back on the account again. 

Here's a direct link to it in case you need it: https://www.plus.net/wizard/?p=view_question&id=175110697